Apparatuses and methods including ferroelectric memory and for accessing ferroelectric memory

ABSTRACT

Apparatuses and methods are disclosed that include ferroelectric memory and for accessing ferroelectric memory. An example method includes increasing a voltage of a first cell plate of a capacitor to change the voltage of a second cell plate of the capacitor, a second digit line, and a second sense node. The voltage of the second cell plate and the second digit line is decreased to change the voltage of the first cell plate, a first digit line, and a first sense node. The first node is driven to a first voltage and the second node is driven to a second voltage responsive to the voltage of the first node being greater than the second node. The first node is driven to the second voltage and the second node is driven to the first voltage responsive to the voltage of the first node being less than the second node.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/131,969 filed Sep. 14, 2018 and issued as U.S. Pat. No. 10,431,283 onOct. 1, 2019, which is a continuation of U.S. patent application Ser.No. 15/679,032 filed. Aug. 16, 2017 and issued as U.S. Pat. No.10,127,972 on Nov. 13, 2018, which application claims the filing benefitof U.S. Provisional Application No. 62/381,900, filed Aug. 31, 2016. Theaforementioned applications, and issued patents, are incorporated byreference herein in their entirety and for any purposes.

BACKGROUND

Memory devices are widely used to store information in variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Information is stored byprogramming different states of a memory device. For example, binarydevices have two states, often denoted by a logic “1” or a logic “0.” Inother systems, more than two states may be stored. To access the storedinformation, the electronic device may read, or sense, the stored statein the memory device. To store information, the electronic device maywrite, or program, the state in the memory device.

Various types of memory devices exist, including random access memory(RAM), read only memory (ROM), dynamic RAM (DRAM), synchronous dynamicRAM (SDRAM), ferroelectric RAM (FeRAM), magnetic RAM (MRAM), resistiveRAM (RRAM), flash memory, and others. Memory devices may be volatile ornon-volatile. Non-volatile memory, e.g., flash memory, can store datafor extended periods of time even in the absence of an external powersource. Volatile memory devices, e.g., DRAM, may lose their stored stateover time unless they are periodically refreshed by an external powersource. A binary memory device may, for example, include a charged ordischarged capacitor. A charged capacitor may, however, becomedischarged over time through leakage currents, resulting in the loss ofthe stored information. Certain features of volatile memory may offerperformance advantages, such as faster read or write speeds, whilefeatures of non-volatile memory, such as the ability to store datawithout periodic refreshing, may be advantageous.

FeRAM may use similar device architectures as volatile memory but mayhave non-volatile properties due to the use of a ferroelectric capacitoras a storage device. FeRAM devices may thus have improved performancecompared to other non-volatile and volatile memory devices. It isdesirable, however, to improve the operation of FeRAM devices. Forexample, it may be desirable to have improved noise resistance duringmemory cell sensing, more compact circuits and reduced layout size, andimproved timing for operation of FeRAM devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example memory array that supportsferroelectric memory in accordance with various embodiments of thepresent disclosure.

FIG. 2A is a schematic diagram of an example circuit that includes acolumn of memory cells according to an embodiment of the presentdisclosure. FIG. 2B is a schematic diagram of a sense componentaccording to an embodiment of the disclosure.

FIG. 3A and FIG. 3B are diagrams of example non-linear electricalproperties for a ferroelectric memory cell in accordance with variousembodiments of the present disclosure.

FIGS. 4A-4E are timing diagrams of various signals during a readoperation according to an embodiment of the disclosure.

FIGS. 5A-5E are timing diagrams of various signals during a readoperation according to an embodiment of the disclosure.

FIG. 6 is a timing diagram of various signals during a write operationaccording to an embodiment of the disclosure.

FIG. 7 is a timing diagram of various signals during a write operationaccording to an embodiment of the disclosure.

FIG. 8 is a diagram depicting a cross-sectional side view of a portionof a memory array showing memory cells according to an embodiment of thedisclosure.

FIG. 9 is a block diagram of a memory array that supports aferroelectric memory in accordance with various embodiments of thepresent disclosure.

FIG. 10 is a block diagram of a system that supports a ferroelectricmemory in accordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION

Certain details are set forth below to provide a sufficientunderstanding of embodiments of the disclosure. However, it will beclear to one skilled in the art that embodiments of the disclosure maybe practiced without these particular details. Moreover, the particularembodiments of the present disclosure described herein are provided byway of example and should not be used to limit the scope of thedisclosure to these particular embodiments. In other instances,well-known circuits, control signals, timing protocols, and softwareoperations have not been shown in detail in order to avoid unnecessarilyobscuring the disclosure.

FIG. 1 illustrates an example memory array 100 that supportsferroelectric memory in accordance with various embodiments of thepresent disclosure. Memory array 100 may also be referred to as anelectronic memory apparatus. Memory array 100 includes memory cells 105that are programmable to store different states. Each state mayrepresent different logic values. For example, for a memory storing twostates, the logic values may be denoted as a logic 0 and a logic 1. Insome cases, memory cell 105 is configured to store more than two logicstates. A memory cell 105 may include a capacitor to store a chargerepresentative of the programmable states. For example, a charged anduncharged capacitor may represent two logic states, respectively.

A ferroelectric memory cell may include a capacitor that has aferroelectric as the dielectric material. Different levels of charge ofa ferroelectric capacitor may represent different logic states.Ferroelectric memory cells 105 may have beneficial properties that mayresult in improved performance relative to other memory architectures,for example, persistent storage of logic states without the need forperiodic refresh operations.

Operations such as reading and writing may be performed on memory cells105 by activating or selecting the appropriate access lines 110 anddigit lines 115. Access lines 110 may also be referred to as word lines110. Activating or selecting a word line 110 or a digit line 115 mayinclude applying a voltage to the respective line. Word lines 110 anddigit lines 115 are made of conductive materials. For example, wordlines 110 and digit lines 115 may be made of metals (such as copper,aluminum, gold, tungsten, etc.), metal alloys, doped semiconductors,other conductive materials, or the like. According to the example ofFIG. 1, each row of memory cells 105 is coupled to word lines 110 WL-CTand WL-CB, and each column of memory cells 105 is coupled to digit lines115 BL-CT and BL-CB. By activating the respective word lines 110 anddigit lines 115 (e.g., applying a voltage to the word lines 110 or digitlines 115), a memory cell 105 may be accessed at their intersection.Accessing the memory cell 105 may include reading or writing the memorycell 105. The intersection of a word lines 110 and digit lines 115 maybe referred to as an address of a memory cell.

In some architectures, the logic storing device of a cell, e.g., acapacitor, may be electrically isolated from the digit lines byselection components. A word line 110 may be coupled to and may controla respective selection component. For example, the selection componentmay be a transistor and the word line 110 may be coupled to the gate ofthe transistor. Activating the word line 110 results in an electricalcoupling or closed circuit between the capacitor of a memory cell 105and corresponding digit line 115. The digit lines may then be accessedto either read or write the memory cell 105.

Accessing memory cells 105 may be controlled through a row decoder 120and a column decoder 130. In some examples, a row decoder 120 receives arow address from the memory controller 140 and activates the appropriateword lines 110 based on the received row address. Similarly, a columndecoder 130 receives a column address from the memory controller 140 andactivates the appropriate digit lines 115. For example, memory array 100may include multiple word lines 110, and multiple digit lines 115. Thus,by activating word lines 110 WL-CT and WL-CB and digit lines 115 BL-CTand BL-CB, the memory cell 105 at their intersection may be accessed.

Upon accessing, a memory cell 105 may be read, or sensed, by sensecomponent 125 to determine the stored state of the memory cell 105. Forexample, after accessing the memory cell 105, the ferroelectriccapacitor of memory cell 105 may discharge onto corresponding digitlines 115. Discharging the ferroelectric capacitor may be based onbiasing, or applying a voltage, to the ferroelectric capacitor. Thedischarging may cause a change in the voltage of the digit lines 115,which sense component 125 may compare to a reference voltage (not shown)in order to determine the stored state of the memory cell 105. Forexample, if a digit line 115 has a higher voltage than the referencevoltage, then sense component 125 may determine that the stored state inmemory cell 105 is a logic 1 and vice versa. Sense component 125 mayinclude various transistors or amplifiers in order to detect (e.g.,compare) and amplify a difference in the signals, which may includelatching the amplified difference. A separate sense component 125 may beprovided for each pair of digit lines BL-CT and BL-CB. The detectedlogic state of memory cell 105 may then be output through column decoder130 as output 135.

A memory cell 105 may be programmed, or written, by activating therelevant word lines 110 and digit lines 115. As discussed above,activating word lines 110 electrically couples the corresponding row ofmemory cells 105 to their respective digit lines 115. By controlling therelevant digit lines 115 while the word lines 110 are activated, amemory cell 105 may be written—e.g., a logic value may be stored in thememory cell 105. Column decoder 130 may accept data, for example input135, to be written to the memory cells 105. A ferroelectric memory cell105 may be written by applying a voltage across the ferroelectriccapacitor. This process is discussed in more detail below.

In some memory architectures, accessing the memory cell 105 may degradeor destroy the stored logic state, and re-write (e.g., restore)operations may be performed to return the original logic state to memorycell 105. For example, the capacitor may be partially or completelydischarged during a sense operation, corrupting the stored logic state.So the logic state may be re-written after a sense operation.Additionally, activating word lines 110 may result in the discharge ofall memory cells in the row. Thus, several or all memory cells 105 inthe row may need to be re-written.

The memory controller 140 may control the operation (e.g., read, write,re-write, etc.) of memory cells 105 through the various components, suchas row decoder 120, column decoder 130, and sense component 125. Memorycontroller 140 may generate row and column address signals in order toactivate the desired word lines 110 and digit lines 115. Memorycontroller 140 may also generate and control various voltage potentialsused during the operation of memory array 100. In general, theamplitude, shape, or duration of an applied voltage discussed herein maybe adjusted or varied and may be different for the various operationsfor operating memory array 100. Furthermore, one, multiple, or allmemory cells 105 within memory array 100 may be accessed simultaneously.For example, multiple or all cells of memory array 100 may be accessedsimultaneously during a reset operation in which all memory cells 105,or a group of memory cells 105, are set to a single logic state.

FIG. 2A illustrates an example circuit 200 that includes a column ofmemory cells according to an embodiment of the present disclosure. FIG.2A illustrates an example circuit 200 that includes memory cells 105 inaccordance with various embodiments of the present disclosure. Circuit200 includes memory cells 105 MC(0)-MC(n), where “n” depends on thearray size. The circuit 200 further includes word linesWL-CT(0)-WL-CT(n) and WL-CB(0)-WL-CB(n), digit lines BL-CT and BL-CB,and sense component 125. The memory cells, word lines, digit lines, andsense component may be examples of memory cells 105, word lines 110,digit lines 115, and sense component 125, respectively, as describedwith reference to FIG. 1. While one column and n rows of memory cells105 are shown in FIG. 2A, a memory array may include many columns androws of memory cells as those shown.

Memory cells 105 may include a logic storage component, such ascapacitor 205 that has a first plate, cell top 230, and a second plate,cell bottom 215. Cell tops 230 and cell bottoms 215 may be capacitivelycoupled through a ferroelectric material positioned between them. Theorientation of cell tops 230 and cell bottoms 215 may be flipped withoutchanging the operation of memory cell 105. The memory cells 105 mayfurther include selection components 220 and 224. The selectioncomponents 220 and 224 may be transistors, for example, n-type fieldeffect transistors. In such an example, each of the memory cells 105includes two transistors and one capacitor (e.g., 2T1C).

Circuit 200 also includes isolation switch 231 and reference switch 233.A reference signal VBLREF is provided to the reference switch 233. Theisolation switch 231 and the reference switch 233 are coupled to a sensenode A of the sense component 125. Activation of the isolation switch231 is controlled by a signal ISO and activation of the reference switch233 is controlled by a signal ISOREF. In some embodiments, the referenceswitch 233 is not included in the circuit 200. For example, inembodiments where the circuit 200 provides on its own reference voltagefor determining the logic value stored by a memory cell 105. In suchembodiments, providing a separate reference voltage (e.g., the voltageVREF of the VBLREF reference signal) to the sense component 125 is notnecessary. Circuit 200 also includes switch 235 and driver circuits 237and 239. In some examples, isolation switch 231, reference switch 233,and switch 235 may be transistors, for example, n-type field effecttransistors, which may be activated by applying a voltage equal to orgreater than its threshold voltage. Activation of the switch 235 iscontrolled by a signal RESTORE. The driver circuit 237 provides a VREADvoltage when activated and the driver circuit 239 provides a groundvoltage (GND) when activated.

Memory cells 105 may be in electronic communication with sense component125 through digit line BL-CT and digit line BL-CB. The switch 235 may becoupled in series between the sense component 125 and the digit lineBL-CT and the driver circuit 237. The switch 235 electrically couples orisolates the sense component 125 from the memory cells 105 and thedriver circuit 237. In the example of FIG. 2A, cell tops 230 may beaccessed via digit line BL-CT and cell bottoms may be accessed via digitline BL-CB. As described above, various states may be stored by chargingor discharging capacitor 205.

The stored state of capacitor 205 may be read or sensed by operatingvarious elements represented in circuit 200. Capacitor 205 may be inelectronic communication with digit lines BL-CB and BL-CT. For example,capacitor 205 can be isolated from digit lines BL-CB and BL-CT whenselection components 220 and 224 are deactivated, and capacitor 205 canbe coupled to digit lines BL-CB and BL-CT when selection components 220and 224 are activated. Activating selection components 220 and 224 maybe referred to as selecting memory cell 105. In some cases, selectioncomponents 220 and 224 are transistors and the operation is controlledby applying voltages to the transistor gates, where the voltagemagnitude is greater than the threshold voltage of the transistors. Wordline WL-CB may activate selection component 220 and word line WL-CT mayactivate selection component 224. For example, a voltage applied to wordline WL-CB is applied to the transistor gate of selection component 220and a voltage applied to word line WL-CT is applied to the transistorgate of selection component 224. As a result, the respective capacitor205 is coupled to digit lines BL-CB and BL-CT, respectively. The memorycell 105 may be considered in storage mode when both word lines WL-CBand WL-CT are deactivated. The memory cell 105 may also be considered instorage mode when both word lines WL-CB and WL-CT are activated and thevoltages of the digit lines BL-CB and BL-CT are the same.

Word lines WL-CB(0)-WL-CB(n) and WL-CT(0)-WL-CT(n) are in electroniccommunication with selection components 220 and 224 of memory cells 105MC(0)-MC(n), respectively. Thus, activating word lines WL-CB and WL-CTof a respective memory cell 105 may activate the memory cell 105. Forexample, activating WL-CB(0) and WL-CT(0) activates memory cell MC(0),activating WL-CB(1) and WL-CT(1) activates memory cell MC(1), and so on.In some examples, the positions of selection components 220 and 224 maybe switched, such that selection component 220 is coupled between digitline BL-CT and cell top 230, and the selection component 224 is coupledbetween digit line BL-CB and cell bottom 215.

Due to the ferroelectric material between the plates of capacitor 205,and as discussed in more detail below, capacitor 205 may not dischargeupon coupling to digit lines BL-CB and BL-CT. To sense the logic statestored by ferroelectric capacitor 205, word lines WL-CB and WL-CT may bebiased to select a respective memory cell 105, and a voltage may beapplied to the digit line BL-CT, for example, by driver circuit 237. Thedigit line BL-CT bias may be applied before or after activatingselection component 224. Biasing the digit line BL-CT may result in avoltage difference across capacitor 205, which may yield a change in thestored charge on capacitor 205. Likewise, biasing the digit line BL-CBmay also result in a voltage difference across capacitor 205, which mayyield a change in the stored charge on capacitor 205. The magnitude ofthe change in stored charge may depend on the initial state of eachcapacitor 205—e.g., whether the initial state stored a logic 1 or alogic 0. When the selection component 220 is activated by the word lineWL-CB, the change in stored charge due to biasing the digit line BL-CTmay cause a change in the voltage of digit line BL-CB based on thecharge stored on capacitor 205. Similarly, when the selection component224 is activated by the word line WL-CT, the change in stored charge dueto biasing the digit line BL-CB may cause a change in the voltage ofdigit line BL-CT based on the charge stored on capacitor 205. The changein the voltage of digit lines BL-CB or BL-CT may cause a change on sensenodes A and B when the isolation switch 231 and switch 235 areactivated, all respectively. The resulting voltage of digit line BL-CBor digit line BL-CT may be compared to a reference voltage by the sensecomponent 125 in order to determine the logic value represented by thestored state of each memory cell 105. In some embodiments, the resultingvoltage of digit line BL-CB or digit line BL-CT may be compared by thesense component 125 to a reference voltage that is a constant voltage,for example, a VREF voltage of the VBLREF signal. In other embodiments,the resulting voltage of digit line BL-CB or digit line BL-CT may becompared by the sense component 125 to a reference voltage that isself-provided, for example, a reference voltage that results frombiasing of the digit lines BL-CB and BL-CT during an access operation.

Sense component 125 may include various transistors or amplifiers todetect and amplify a difference in signals, which may including latchingthe amplified difference. Sense component 125 may include a senseamplifier that receives and compares the voltage of either of its sensenodes (e.g., sense nodes A or B) and the voltage of the reference signalVBLREF, which may be a reference voltage. In some embodiments, thevoltage of either of the sense nodes may be compared to a self-providedreference voltage. The voltages of the sense nodes A and B may beaffected by the voltages of the digit lines BL-CB and BL-CT,respectively, for example, when the sense node A is coupled to the digitline BL-CB and when the sense node B is coupled to the digit line BL-CT.The sense amplifier output (e.g., sense node) may be driven to thehigher (e.g., a positive) or lower (e.g., negative or ground) supplyvoltage based on the comparison and the other sense node may be drivento the complementary voltage (e.g., the positive supply voltage iscomplementary to the negative or ground voltage, and the negative orground voltage is complementary to the positive supply voltage). Forinstance, if the sense node B has a higher voltage than reference signalVBLREF or a higher voltage than a self-provided reference voltage, thenthe sense amplifier may drive the sense node B to a positive supplyvoltage and drive the sense node A to a negative or ground voltage.Sense component 125 may latch the state of the sense amplifier (e.g.,voltages of sense node A and/or sense node B and/or the voltages ofdigit lines BL-CB and/or BL-CT), which may be used to determine thestored state and logic value of memory cell 105, e.g., logic 1.Alternatively, if the sense node B has a lower voltage than referencesignal VBLREF or lower voltage than a self-provided reference voltage,the sense amplifier may drive the sense node B to a negative or groundvoltage and drive the sense node A to a positive supply voltage. Sensecomponent 125 may also latch the sense amplifier state for determiningthe stored state and the logic value of memory cell 105, e.g., logic 0.The stored state may represent a logic value of memory cell 105, whichmay then be output, for example, through column decoder 130 as output135 with reference to FIG. 1. In embodiments where the sense component125 also drives the digit lines BL-CB and BL-CT to complementaryvoltages, the complementary voltages may be applied to the memory cell105 to restore the original data state read. By restoring the data, aseparate restore operation is unnecessary.

As previously described, the word lines WL-CB and WL-CT and theselection components 220 and 224 provide independent control of cellbottom 215 and cell top 230 of the capacitor 205, thus, removing theneed for a shared cell plate, as is typical with conventionalferroelectric memories. As a result, the cells may be less susceptibleto disturb mechanisms, for example, cell plate related pattern noise.Additionally, cell plate driver circuits, which are needed for sharedcell plate designs, are not needed which can reduce circuit size. Thedigit lines of the plurality of columns of memory cells may be driven tovoltages independently of one another. For example, the digit line BL-CT(the digit line coupled through a selection component to the cell top,which is opposite of the cell bottom) of a first column of memory cellsmay be driven to a voltage independently of the voltage to which thedigit line BL-CT of a second column of memory cells are driven.

FIG. 2B illustrates a sense component 125 according to an embodiment ofthe disclosure. The sense component 125 includes p-type field effecttransistors 252 and 256 and n-type field effect transistors 262 and 266.Gates of the transistor 252 and transistor 262 are coupled to sense nodeA. Gates of the transistor 256 and transistor 266 are coupled to sensenode B. The transistors 252 and 256, and the transistors 262 and 266represent a sense amplifier. A p-type field effect transistor 258 isconfigured to be coupled to a power supply (e.g., VREAD voltage powersupply) and is coupled to a common node of the transistors 252 and 256.The transistor 258 is activated by an active PSA signal (e.g., activelow logic). An n-type field effect transistor 268 is configured to becoupled to a sense amplifier reference voltage (e.g., ground) and iscoupled to a common node of the transistors 262 and 266. The transistor268 is activated by an active NSA signal (e.g., active high logic).Reference switch 233 coupled to sense node A is also shown in FIG. 2B. Areference signal VBLREF is provided to the reference switch 233.Activation of the reference switch 233 is controlled by a signal ISOREF.As previously described, in some embodiments, the reference switch 233is not included in the circuit 200, such as in embodiments where thecircuit 200 provides on its own reference voltage for determining thelogic value stored by a memory cell 105. In such embodiments, providinga separate reference voltage (e.g., the voltage VREF of the VBLREFreference signal) to the sense component 125 is not necessary.

In operation, the sense amplifier is activated by activating the PSA andNSA signals to couple the sense amplifier to the voltage of the powersupply and the sense amplifier reference voltage. When activated, thesense amplifier compares the voltages of sense nodes A and B, andamplifies a voltage difference by driving the sense nodes A and B tocomplementary voltage levels (e.g., driving sense node A to VREAD andsense node B to ground, or driving sense node A to ground and sense nodeB to VREAD). When the sense nodes A and B have been driven to thecomplementary voltage levels, the voltages of sense nodes A and B arelatched by the sense amplifier and remain latched until the senseamplifier is deactivated.

With reference to FIG. 2A, to write memory cell 105, a voltage may beapplied across capacitor 205. Various methods may be used. In someexamples, selection components 220 and 224 may be activated through wordlines WL-CB and WL-CT, respectively, in order to electrically couplecapacitor 205 to digit lines BL-CB and BL-CT. For a ferroelectriccapacitor 205, a voltage may be applied across capacitor 205 bycontrolling the voltage of cell top 230 (through digit line BL-CT) andcell bottom 215 (through digit line BL-CB) to apply a positive ornegative voltage across the capacitor 205.

In some examples, a restore operation may be performed after sensing. Aspreviously discussed, the sense operation may degrade or destroy theoriginally stored state of the memory cell 105. After sensing, the statemay be written back to the memory cell 105. For example, sense component125 may determine the stored state of memory cell 105 and may then writethe same state back, for example, through isolation switch 231 andswitch 235.

Ferroelectric materials have non-linear polarization properties. FIG. 3Aand FIG. 3B illustrate examples of non-linear electrical properties withhysteresis curves 300-a (FIG. 3A) and 300-b (FIG. 3B) for a memory cellfor ferroelectric memory in accordance with various embodiments of thepresent disclosure. Hysteresis curves 300-a and 300-b illustrate anexample ferroelectric memory cell writing and reading process,respectively. Hysteresis curves 300 depict the charge, Q, stored on aferroelectric capacitor (e.g., capacitor 205 of FIG. 2A) as a functionof a voltage difference, V.

A ferroelectric material is characterized by a spontaneous electricpolarization, for example, it maintains a non-zero electric polarizationin the absence of an electric field. Example ferroelectric materialsinclude barium titanate (BaTiO₃), lead titanate (PbTiO₃), lead zirconiumtitanate (PZT), and strontium bismuth tantalate (SBT). The ferroelectriccapacitors described herein may include these or other ferroelectricmaterials. Electric polarization within a ferroelectric capacitorresults in a net charge at the ferroelectric material's surface andattracts opposite charge through the capacitor terminals. Thus, chargeis stored at the interface of the ferroelectric material and thecapacitor terminals. Because the electric polarization may be maintainedin the absence of an externally applied electric field for relativelylong times, even indefinitely, charge leakage may be significantlydecreased as compared with, for example, capacitors employed in volatilememory arrays. This may reduce the need to perform refresh operations asdescribed above for some volatile memory architectures.

Hysteresis curves 300 may be understood from the perspective of a singleterminal of a capacitor. By way of example, if the ferroelectricmaterial has a negative polarization, positive charge accumulates at theterminal. Likewise, if the ferroelectric material has a positivepolarization, negative charge accumulates at the terminal. Additionally,it should be understood that the voltages in hysteresis curves 300represent a voltage difference across the capacitor and are directional.For example, a positive voltage may be realized by applying a positivevoltage to the terminal in question (e.g., a cell top 230) andmaintaining the second terminal (e.g., a cell bottom 215) at ground (orapproximately zero volts (0V)). A negative voltage may be applied bymaintaining the terminal in question at ground and applying a positivevoltage to the second terminal, for example, positive voltages may beapplied to negatively polarize the terminal in question. Similarly, twopositive voltages, two negative voltages, or any combination of positiveand negative voltages may be applied to the appropriate capacitorterminals to generate the voltage difference shown in hysteresis curves300.

As depicted in hysteresis curve 300-a, the ferroelectric material maymaintain a positive or negative polarization with a zero voltagedifference, resulting in two possible charged states: charge state 305and charge state 310. According to the example of FIG. 3, charge state305 represents a logic 0 and charge state 310 represents a logic 1. Insome examples, the logic values of the respective charge states may bereversed without loss of understanding.

A logic 0 or 1 may be written to the memory cell by controlling theelectric polarization of the ferroelectric material, and thus the chargeon the capacitor terminals, by applying voltage. For example, applying anet positive voltage 315 across the capacitor results in chargeaccumulation until charge state 305-a is reached. Upon removing voltage315, charge state 305-a follows path 320 until it reaches charge state305 at zero voltage potential. Similarly, charge state 310 is written byapplying a net negative voltage 325, which results in charge state310-a. After removing negative voltage 325, charge state 310-a followspath 330 until it reaches charge state 310 at zero voltage. Chargestates 305 and 310 may also be referred to as the remnant polarization(Pr) values, which is the polarization (or charge) that remains uponremoving the external bias (e.g., voltage).

To read, or sense, the stored state of the ferroelectric capacitor, avoltage may be applied across the capacitor. In response, the storedcharge, Q, changes, and the degree of the change depends on the initialcharge state, and as a result, the final stored charge (Q) depends onwhether charge state 305-b or 310-b was initially stored. For example,hysteresis curve 300-b illustrates two possible stored charge states305-b and 310-b. Voltage 335 may be applied across the capacitor aspreviously discussed. Although depicted as a positive voltage, voltage335 may be negative. In response to voltage 335, charge state 305-b mayfollow path 340. Likewise, if charge state 310-b was initially stored,then it follows path 345. The final position of charge state 305-c andcharge state 310-c depend on a number of factors, including the specificsensing scheme and circuitry.

In some cases, the final charge may depend on the intrinsic capacitanceof the digit line coupled to the memory cell. For example, if thecapacitor is electrically coupled to the digit line and voltage 335 isapplied, the voltage of the digit line may rise due to its intrinsiccapacitance. So a voltage measured at a sense component may not equalvoltage 335 and instead may depend on the voltage of the digit line. Theposition of final charge states 305-c and 310-c on hysteresis curve300-b may thus depend on the capacitance of the digit line and may bedetermined through a load-line analysis. Charge states 305-c and 310-cmay be defined with respect to the digit line capacitance. As a result,the voltage of the capacitor, voltage 350 or voltage 355, may bedifferent and may depend on the initial state of the capacitor.

By comparing the digit line voltage to a reference voltage, the initialstate of the capacitor may be determined. The digit line voltage may bethe difference between voltage 335 and the final voltage across thecapacitor, voltage 350 or voltage 355 (e.g., voltage 335-voltage 350) or(e.g., voltage 335-voltage 355). A reference voltage may be generatedsuch that its magnitude is between the two possible digit line voltagesin order to determine the stored logic state, for example, if the digitline voltage is higher or lower than the reference voltage. For example,the reference voltage may be an average of the two quantities (voltage335-voltage 350) and (voltage 335-voltage 355). In another example, thereference voltage may be provided by isolating a voltage on first sensenode of a sense component, then causing a voltage change on a secondsense node of the sense component through a digit line, and comparingthe resulting voltage of the second sense node with the isolated voltageof the first sense node. Upon comparison by the sense component, thesensed digit line voltage may be determined to be higher or lower thanthe reference voltage, and the stored logic value of the ferroelectricmemory cell (e.g., a logic 0 or 1) may be determined.

FIGS. 4A-4E are timing diagrams of various signals during a readoperation according to an embodiment of the disclosure. FIGS. 4A-4E willbe described with reference to memory array 100 and example circuit 200of FIGS. 1 and 2. The example read operation of FIGS. 4A-4E may provideincreased voltage margin relative to a reference voltage used todetermine the stored state (and the corresponding logic value) of amemory cell.

Prior to time T0 the digit line BL-CB is coupled to the sense node A ofthe sense component 125 through an activated isolation switch 231. Theswitch 235 is deactivated so that the voltage of the digit line BL-CTand the voltage of the sense node B are independent of one another. Thedigit line BL-CB and sense node A, and the digit line BL-CT and sensenode B are all precharged to a voltage, such as ground. At time T0, theword line WL-CB is activated to activate the selection component 220 tocouple the cell bottom 215 to the digit line BL-CB. At time T1 thedriver circuit 237 is enabled to drive a voltage VREAD onto the digitline BL-CT. The word line WL-CT is activated at time T2 to activate theselection component 224 to couple the cell top 230 to the digit lineBL-CT (FIG. 4A).

The voltage VREAD is applied to the cell top 230 through the activatedselection component 224 to cause a voltage change at the cell bottom215. As previously discussed, the magnitude of the change in voltagecaused at the cell bottom 215 is based at least in part on the chargestate initially stored by the capacitor 205. The voltage change at thecell bottom 215 from an initial voltage to an increased voltage alsocauses the voltage of the digit line BL-CB and the sense node A tochange as well. Where the initial charge state represents a logic 1, thesense node A (SENSEA-1 in FIG. 4C) and the digit line BL-CB (BL-CB-1 inFIG. 4B) change from ground (e.g., the initial voltage) to a firstvoltage (e.g., the increased voltage) (FIG. 4C). Where the initialcharge state represents a logic 0, the sense node A (SENSEA-0 in FIG.4E) and the digit line BL-CB (BL-CB-0 in FIG. 4D) change from ground(e.g., the initial voltage) to a second voltage (e.g., the increasedvoltage). In the example shown in FIGS. 4A-4E, the first voltage isgreater than the second voltage.

The switch 235 is still not active at time T2, and thus, the digit lineBL-CT and sense node B are not coupled through an active switch 235.Nonetheless, coupling the voltage VREAD at time T2 to the cell top 230through the digit line BL-CT and the activated selection component 224also causes the voltage of sense node B to change. Where the initialcharge state represents a logic 1, the sense node B (SENSEB-1 in FIG.4C) changes from ground to a third voltage. Where the initial chargestate represents a logic 0, the sense node B (SENSEB-0 in FIG. 4D)changes from ground to a fourth voltage. In the example shown in FIG. 4,the third voltage is greater than the fourth voltage, and both the thirdand fourth voltages are less than the second voltage. The voltages ofsense node A, sense node B, and the digit line BL-CB develop betweentime T2 and T3.

At time T3 the isolation switch 231 is deactivated so that the sensenode A is isolated from the digit line BL-CB (FIG. 4A) and the switch235 is activated by the signal RESTORE to conduct voltage between thesense node B and the digit line BL-CT. The reference switch 233 is thenactivated to provide a voltage VREF of a reference signal VBLREF to thesense node A. The voltage VREF of the reference signal VBLREF is aconstant (e.g., fixed) voltage. As a result, the voltage of sense node Achanges from the first or second voltage to the voltage VREF by thereference signal VBLREF (FIGS. 4C and 4E). The sense node B is coupledto the digit line BL-CT through the activated switch 235, which causesthe voltage of sense node B to change from the third or fourth voltageto the voltage VREAD, which is the voltage of the digit line BL-CT(FIGS. 4C and 4E).

The driver circuit 239 is enabled at time T4 to drive the digit lineBL-CB to ground, which causes the cell bottom 215 to also change toground. The voltage of the digit line BL-CB may change from the firstvoltage (due to the initial charge state of the capacitor 205corresponding to logic 1) to ground (FIG. 4B), or from the secondvoltage (due to the initial charge state of the capacitor 205corresponding to logic 0) to ground (FIG. 4D). The change in voltagefrom the first voltage to ground is greater than the change in voltagefrom the second voltage to ground.

The change in voltage of the cell bottom 215 due to the digit line BL-CBbeing driven to ground is coupled across the capacitor 205 to cause achange in voltage of the cell top 230. With the sense node B coupled tothe cell top 230 through activated selection component 224, digit lineBL-CT, and activated switch 235, the change in voltage causes thevoltage of the sense node B to change as well. The change in voltage ofsense node B will depend on the change in voltage of the digit lineBL-CB. For example, where the change in voltage of the digit line BL-CBis from the first voltage to ground, the voltage of sense node B changesfrom the VREAD voltage to a fifth voltage (FIG. 4C) that is less thanthe voltage VREF of the VBLREF signal applied to sense node A. Where thechange in voltage of the digit line BL-CB is from the second voltage toground, the voltage of sense node B changes from the VREAD voltage to asixth voltage (SENSEB-0) that is greater than the voltage VREF of theVBLREF signal applied to sense node A.

Prior to time T5 the switch 235 is deactivated by the signal RESTORE toisolate the sense node B from the digit line BL-CT. At time T5 the sensecomponent 125 is activated and the isolation switch 231 is activated tocouple the sense node A to the digit line BL-CB. Also at time T5, orshortly thereafter, the switch 235 is activated to couple the sense nodeB to the digit line BL-CT. With the sense component 125 activated, avoltage difference between the sense node A and sense node B is detectedand amplified to drive the sense nodes to complementary voltages (e.g.,VREAD and ground). The digit lines BL-CB and BL-CT are likewise drivento complementary voltages by the sense component 125 through theactivated isolation switch 231 and the activated switch 235. Forexample, where the voltage of sense node B is less than the voltage VREFof sense node A (e.g., sense node B at the fifth voltage (SENSEB-1 inFIG. 4C)), the activated sense component 125 drives the sense node B(and digit line BL-CT) to ground and the sense node A (and digit lineBL-CB) to voltage VREAD. In contrast, where the voltage of sense node Bis greater than the VREF voltage of sense node A (e.g., sense node B atthe sixth voltage (SENSEB-0 in FIG. 4E)), the activated sense component125 drives the sense node B (and digit line BL-CT) to voltage VREAD andthe sense node A (and digit line BL-CB) to ground FIG. 4E. The voltagesof the sense node A and sense node B are latched by the sense component125 after being driven to complementary voltages. The latched voltagesof the sense nodes A and B represent a corresponding logic value, whichmay be output, for example, through column decoder 130 as output 135(FIG. 1).

Also at time T5 or after time T5 the isolation switch 231 is activatedto couple the sense node A to the digit line BL-CB (FIG. 4A). Sense nodeB is coupled to the digit line BL-CT through the activated switch 235.As a result, the driving of the sense nodes A and B to complementaryvoltages by the sense component 125 also drives the digit lines BL-CBand BL-CT to the corresponding complementary voltages. Similarly, thedriving of the digit lines BL-CB and BL-CT also drives the cell bottom215 and cell top 230 to the complementary voltages.

For example, driving the sense node B to ground and the sense node A tothe voltage VREAD (FIG. 4C) also drives the digit line BL-CT and celltop 230 to ground and drives the digit line BL-CB and cell bottom 215 tothe voltage VREAD (FIG. 4B). Driving the sense node B to voltage VREADand the sense node A to ground (FIG. 4E) also drives the digit lineBL-CT and the cell top 230 to voltage VREAD and drives the digit lineBL-CB and the cell bottom 215 to ground (FIG. 4D). Driving thecomplementary voltages to the cell top 230 and the cell bottom 215ensures that the read operation does not change or degrade the originalcharge state of the capacitor 205 by restoring the original charge stateof the capacitor 205.

The sense component 125 is deactivated at time T6 and the voltages ofsense nodes A and B, and digit lines BL-CB and BL-CT are driven toground. The word lines WL-CB and WL-CT are deactivated at time T7 (FIG.4A) to deactivate the selection components 220 and 224 to isolate thecapacitor 205 from the digit lines BL-CB and BL-CT, all respectively, tocomplete the read operation.

FIGS. 5A-5E are timing diagrams of various signals during a readoperation according to an embodiment of the disclosure. FIGS. 5A-5E willbe described with reference to memory array 100 and example circuit 200of FIGS. 1 and 2. As will be described in more detail below, the readoperation of FIGS. 5A-5E relies on self-provided reference voltage fordetermining the logic value stored by a memory cell. Thus, a separatereference voltage for this purpose is not needed in the example readoperation of FIGS. 5A-5E, which may reduce circuit complexity andimprove circuit density. For example, self-provided (e.g., locallycreated) reference voltages may allow for eliminating two transistorsfrom the sense component, and may allow for eliminating reference ampsand a reference distribution network. Additionally, self-providedreference voltages may be beneficial because ferroelectric memory cellsare subject to cycling, imprinting and sensitivity of temperaturevariations affecting a sense window relative to a constant referencevoltage.

Prior to time T0 the digit line BL-CB is coupled to the sense node A ofthe sense component 125 through an active isolation switch 231. Thedigit line BL-CB and sense node A, and the digit line BL-CT and sensenode B are all precharged to a reference voltage, such as ground. Attime T0, the word line WL-CB is activated to activate the selectioncomponent 220 to couple the digit line BL-CB to the cell bottom 215. Attime T1 the driver circuit 237 is enabled to drive a voltage VREAD ontothe digit line BL-CT. The word line WL-CT is activated at time T2 toactivate the selection component 224 to couple the digit line BL-CT tothe cell top 230 (FIG. 5A).

The voltage VREAD is applied to the cell top 230 through the activatedselection component 224 to cause a voltage change at the cell bottom215. As previously discussed, the magnitude of the change in voltagecaused at the cell bottom 215 is based at least in part on the chargestate initially stored by the capacitor 205. The voltage change at thecell bottom 215 also causes the voltage of the digit line BL-CB and thesense node A to change as well. Where the initial charge staterepresents a logic 1, the sense node A (SENSEA-1 in FIG. 5C) and thedigit line BL-CB (BL-CB-1 in FIG. 5B) change from ground to a firstvoltage. Where the initial charge state represents a logic 0, the sensenode A (SENSEA-0 in FIG. 5E) and the digit line BL-CB (BL-CB-0 in FIG.5D) change from ground to a second voltage. In the example shown inFIGS. 5B-5E, the first voltage is greater than the second voltage.

The switch 235 is still not active at time T2, and thus, the digit lineBL-CT and sense node B are not coupled through an active switch 235.Nonetheless, coupling the voltage VREAD at time T2 to the cell top 230through the digit line BL-CT and the activated selection component 224also causes the voltage of sense node B to change. Where the initialcharge state represents a logic 1, the sense node B (SENSEB-1 in FIG.5C) changes from ground to a third voltage. Where the initial chargestate represents a logic 0, the sense node B (SENSEB-0 in FIG. 5D)changes from ground to a fourth voltage. In the example shown in FIG. 5,the third voltage is greater than the fourth voltage, and both the thirdand fourth voltages are less than the second voltage. The voltages ofsense node A, sense node B, and the digit line BL-CB develop betweentime T2 and T3.

At time T3 the isolation switch 231 is deactivated so that the sensenode A is isolated from the digit line BL-CB in FIG. 5A and the switch235 is activated by the signal RESTORE to conduct voltage between thesense node B and the digit line BL-CT. As a result, the voltage of sensenode A may change without changing the voltage of digit line BL-CB, andvice versa. With the switch 235 activated to couple the sense node B tothe digit line BL-CT, the voltage of sense node B changes from the thirdor fourth voltage to the voltage VREAD, which is the voltage of thedigit line BL-CT (FIGS. 5C and 5E). With the isolation switch 231deactivated, the digit line BL-CB remains at the first or second voltageand the sense node A increases relative to the first or second voltages(FIGS. 5C and 5E).

The driver circuit 239 is enabled at time T4 to drive the digit lineBL-CB to ground, which causes the cell bottom 215 to also change toground. The voltage of the digit line BL-CB may change from the firstvoltage (due to the initial charge state of the capacitor 205corresponding to logic 1) to ground (FIG. 5B), or from the secondvoltage (due to the initial charge state of the capacitor 205corresponding to logic 0) to ground (FIG. 5D). The change in voltagefrom the first voltage to ground is greater than the change in voltagefrom the second voltage to ground. The change in voltage of the digitline BL-CB also causes the voltage of the sense node A to change. Wherethe sense node A is at a voltage increased relative to the firstvoltage, the voltage of sense node A (SENSEA-1 in FIG. 5C) changes to afifth voltage due to the digit line BL-CB being driven to ground. Wherethe sense node A is at a voltage increased relative to the secondvoltage, the voltage of sense node A (SENSEA-0 in FIG. 5E) changes to asixth voltage due to the digit line BL-CB being driven to ground.

The change in voltage of the cell bottom 215 due to the digit line BL-CBbeing driven to ground is coupled across the capacitor 205 to cause achange in voltage of the cell top 230. With the sense node B coupled tothe cell top 230 through activated selection component 224, digit lineBL-CT, and activated switch 235, the change in voltage causes thevoltage of the sense node B to change as well. The change in voltage ofsense node B will depend on the change in voltage of the digit lineBL-CB. For example, where the change in voltage of the digit line BL-CBis from the first voltage to ground, the voltage of sense node B changesfrom the VREAD voltage to a seventh voltage (SENSEB-1 in FIG. 5C) thatis less than the fifth voltage of the sense node A (SENSEA-1 in FIG.5C). Where the change in voltage of the digit line BL-CB is from thesecond voltage to ground, the voltage of sense node B changes from theVREAD voltage to an eighth voltage (SENSEB-0 in FIG. 5E) that is greaterthan the sixth voltage of the sense node A (SENSEA-0 in FIG. 5E).

Prior to time T5 the switch 235 is deactivated by the signal RESTORE toisolate the sense node B from the digit line BL-CT. At time T5 the sensecomponent 125 is activated, and a voltage difference between the sensenode A and sense node B is detected and amplified to drive the sensenodes to complementary voltages (e.g., VREAD and ground). The voltage atthe sense node A represents a reference voltage against which thevoltage at the sense node B is compared. The reference voltage at sensenode A is self-provided, and is based on the voltage of the cell bottom215 resulting from driving the voltage VREAD to the cell top 230 overthe digit line BL-CT at time T1. Where the voltage of sense node B isless than the voltage of sense node A (e.g., sense node B at the seventhvoltage (SENSEB-1 in FIG. 5C) and sense node A at the fifth voltage(SENSEA-1 in FIG. 5C)), the activated sense component 125 drives thesense node B to ground and the sense node A to voltage VREAD. Incontrast, where the voltage of sense node B is greater than the voltageof sense node A (e.g., sense node B at the eighth voltage (SENSEB-0 inFIG. 5E) and sense node A at the sixth voltage (SENSEA-0 in FIG. 5E)),the activated sense component 125 drives the sense node B to voltageVREAD and the sense node A to ground. The voltages of the sense node Aand sense node B are latched by the sense component 125 after beingdriven to complementary voltages. The latched voltages of the sensenodes A and B represent a corresponding logic value, which may beoutput, for example, through column decoder 130 as output 135 (FIG. 1).

Also at time T5 or after time T5 the isolation switch 231 is activatedto couple the sense node A to the digit line BL-CB and the switch 235 isactivated to couple the sense node B to the digit line BL-CT (FIG. 5A).Sense node B is coupled to the digit line BL-CT through the activatedswitch 235. As a result, the driving of the sense nodes A and B tocomplementary voltages by the sense component 125 also drives the digitlines BL-CB and BL-CT to the corresponding complementary voltages.Similarly, the driving of the digit lines BL-CB and BL-CT also drivesthe cell bottom 215 and cell top 230 to the complementary voltages.

For example, driving the sense node B to ground and the sense node A tothe voltage VREAD (FIG. 5C) also drives the digit line BL-CT and celltop 230 to ground and drives the digit line BL-CB and cell bottom 215 tothe voltage VREAD (FIG. 5B). Driving the sense node B to voltage VREADand the sense node A to ground (FIG. 5E) also drives the digit lineBL-CT and the cell top 230 to voltage VREAD and drives the digit lineBL-CB and the cell bottom 215 to ground (FIG. 5D). Driving thecomplementary voltages to the cell top 230 and the cell bottom 215ensures that the read operation does not change or degrade the originalcharge state of the capacitor 205 by restoring the original charge stateof the capacitor 205.

The sense component 125 is deactivated at time T6 and the voltages ofsense nodes A and B, and digit lines BL-CB and BL-CT are driven toground. The word lines WL-CB and WL-CT are deactivated at time T7 (FIG.5A) to deactivate the selection components 220 and 224 to isolate thecapacitor 205 from the digit lines BL-CB and BL-CT, all respectively, tocomplete the read operation.

Embodiments of read operations disclosed, for example, the readoperations described with reference to FIGS. 4A-4E and 5A-5E, mayincrease a sense window for reading ferroelectric memory cells, andavoids spending additional power to bump a capacitor plate to a highervoltage during the read operation. In contrast, power spent on initiallydriving a capacitor plate (e.g., to the VREAD voltage), may be recycledto increase the sense window.

FIG. 6 is a timing diagram of various signals during a write operationaccording to an embodiment of the disclosure. FIG. 6 will be describedwith reference to memory array 100 and example circuit 200 of FIGS. 1and 2. In the example write operation of FIG. 6 a logic “0” is writtento a memory cell 105 that currently stores a logic “1”.

Prior to time TA, the word lines WL-CB and WL-CT are activated toactivate selection components 220 and 224, respectively. As a result,the digit line BL-CB is coupled to cell bottom 215 and the digit lineBL-CT is coupled to cell top 230 of the capacitor 205. The voltage ofthe digit line BL-CB is at the VREAD voltage representing the currentlystored logic “1” and the voltage of the digit line BL-CT is at areference voltage, for example, ground. Also prior to time TA, the digitline BL-CB is coupled to sense node A of the sense component 125 throughactivated isolation switch 231, and the digit line BL-CT is coupled tosense node B of the sense component 125 through activated switch 235.Thus, prior to time TA, the sense nodes A and B are coupled to cellbottom 215 and cell top 230, respectively.

At time TA, a write amplifier (not shown) coupled to sense nodes A and Bdrives the sense node A from the VREAD voltage to ground and drivessense node B from ground to the VREAD voltage. The voltages of sensenodes A and B are latched by the sense component 125. With the sensenodes A and B driven by the write amplifier, the voltage of the digitline BL-CB changes to ground and the voltage of the digit line BL-CTchanges to the VREAD voltage. The ground voltage of the sense node A andthe digit line BL-CB represents the logic “0” written to the capacitor205. The ground voltage of the digit line BL-CB and the VREAD voltage ofthe digit line BL-CT are applied to the cell bottom 215 and to the celltop 230 through the activated selection components 220 and 224, allrespectively. As a result, the capacitor 205 becomes polarized in anopposite polarization to change the stored state data from representinga logic “1” to a logic “0”.

By time TB the voltages at the sense nodes A and B have been latched bythe sense component 125 and the voltages of the sense nodes A and B areno longer driven by the write amplifier. The sense component 125 isdeactivated at time TB and the voltage of the sense node B (and thedigit line BL-CT) changes to ground. With both cell top 230 and the cellbottom 215 at the same voltage, the word lines WL-CB and WL-CT aredeactivated at time TC to complete the write operation.

FIG. 7 is a timing diagram of various signals during a write operationaccording to an embodiment of the disclosure. FIG. 7 will be describedwith reference to memory array 100 and example circuit 200 of FIGS. 1and 2. In the example write operation of FIG. 7 a logic “1” is writtento a memory cell 105 that currently stores a logic “0”.

Prior to time TA, the word lines WL-CB and WL-CT are activated toactivate selection components 220 and 224, respectively. As a result,the digit line BL-CB is coupled to cell bottom 215 and the digit lineBL-CT is coupled to cell top 230 of the capacitor 205. The voltage ofthe digit line BL-CB is at ground representing the currently storedlogic “0” and the voltage of the digit line BL-CT is at the VREADvoltage. Also prior to time TA, the digit line BL-CB is coupled to sensenode A of the sense component 125 through activated isolation switch231, and the digit line BL-CT is coupled to sense node B of the sensecomponent 125 through activated switch 235. Thus, prior to time TA, thesense nodes A and B are coupled to cell bottom 215 and cell top 230,respectively.

At time TA, a write amplifier (not shown) coupled to sense nodes A and Bdrives the sense node A from ground to the VREAD voltage and drivessense node B from the VREAD voltage to ground. The voltages of sensenodes A and B are latched by the sense component 125. With the sensenodes A and B driven by the write amplifier, the voltage of the digitline BL-CB changes to the VREAD voltage and the voltage of the digitline BL-CT changes ground. The VREAD voltage of the sense node A and thedigit line BL-CB represents the logic “1” written to the capacitor 205.The VREAD voltage of the digit line BL-CB and the ground voltage of thedigit line BL-CT are applied to the cell bottom 215 and to the cell top230 through the activated selection components 220 and 224, allrespectively. As a result, the capacitor 205 becomes polarized in anopposite polarization to change the stored state from representing alogic “0” to a logic “1”.

By time TB the voltages at the sense nodes A and B have been latched bythe sense component 125 and the voltages of the sense nodes A and B areno longer driven by the write amplifier. The sense component 125 isdeactivated at time TB and the voltage of the sense node B (and thedigit line BL-CT) changes to ground. With both cell top 230 and the cellbottom 215 at the same voltage, the word lines WL-CB and WL-CT aredeactivated at time TC to complete the write operation.

In some embodiments, the write operations described with reference toFIGS. 6 and 7 may be performed in conjunction with a read operation, forexample, read operations described with reference to FIGS. 4A-4E and5A-5E. For example, with reference to the example read operation ofFIGS. 4A-4E and 5A-5E, the example write operation of FIG. 6 may beperformed following the sense component 125 driving the sense nodes Aand B, digit lines BL-CB and BL-CT, and cell bottom 215 and cell top 230to complementary voltages (e.g., following time T5 of FIGS. 4A-4E and5A-5E) and when the memory cell 105 stores a logic 1 (e.g., BL-CB andcell bottom 215 at the voltage VREAD and BL-CT and cell top 230 atground). In another example, with reference to the example readoperation of FIGS. 4A-4E and 5A-5E, the example write operation of FIG.7 may be performed following the sense component 125 driving the sensenodes A and B, digit lines BL-CB and BL-CT, and cell bottom 215 and celltop 230 to complementary voltages (e.g., following time T5) and when thememory cell 105 stores a logic 0 (e.g., BL-CB and cell bottom 215 atground and BL-CT and cell top 230 at the VREAD voltage). The examplewrite operations of FIGS. 6 and 7 may be performed in conjunction withdifferent operations in other embodiments.

As previously described with reference to FIGS. 4 and 5, a logic “1” isrepresented by a voltage on the cell bottom greater than the referencevoltage (e.g., the VREF voltage of the reference signal VBLREF,self-provided reference voltage, etc.) and a logic “0” is represented bya voltage on the cell bottom less than the reference voltage. As alsopreviously described with reference to the example write operations ofFIGS. 6 and 7 a logic “1” is written by applying the VREAD voltage tothe cell bottom and ground to the cell top, and a logic “0” is writtenby applying ground to the cell bottom and the VREAD voltage to the celltop. In some examples, the logic values corresponding to the voltagesrelative to the reference voltage, and the application of the netpositive/negative voltages for writing the logic values may be reversedwithout departing from the scope of the disclosure.

The example voltages and signal timing described with reference to theread and write operations of FIGS. 4-7 have been provided forillustrative purposes, and are not intended to limit the scope of thepresent disclosure. It will be appreciated that the voltages andrelative signal timing may be modified without departing from the scopeof the present disclosure.

FIG. 8 illustrates a portion of a memory array 100 including an exampleembodiment of memory cells 105 according to the disclosure.

The illustrated region of memory array 100 includes digit lines BL-CTand BL-CB. The digit lines BL-CT and BL-CB are vertically offsetrelative to another and may be connected to a sense component 125. Apair of adjacent memory cells 105 are shown, with such adjacent memorycells being in a common column as one another within the memory array(e.g., being along a common column represented by digit lines BL-CT andBL-CB). Insulative material 48 is shown to surround the variouscomponents of memory cells 105. In some embodiments the memory cells 105may be referred to as substantially identical memory cells along acolumn of a memory array, with the term “substantially identical”meaning that the memory cells are identical to one another withinreasonable tolerances of fabrication and measurement.

The digit line BL-CB is shown to be over and supported by a base 15.Such base may be a semiconductor material. The memory cells 105 eachincludes selection components 220 and 224 and a ferroelectric capacitor205. The capacitor 205 is vertically between the selection components220 and 224 of memory cell 105. The capacitor 205 includes a firstplate, cell top 230, and a second plate, cell bottom 215, and aferroelectric material 232 disposed between the cell top 230 and thecell bottom 215. Although the cell top 230 is shown to becontainer-shaped and the cell bottom 215 is shown to extend within suchcontainer shape, in other embodiments the cell top and bottom may haveother configurations. For instance, the cell top and bottom may haveplanar configurations. Pillar 212 extends from digit line BL-CT to thecell top 230 of capacitor 205, and the pillar 202 extends from the digitline BL-CB to the cell bottom 215 of capacitor 205.

The selection component 224 has source/drain region 214 extending to thecell top 230 of capacitor 205, and has source/drain region 216 extendingto the digit line BL-CT. The selection component 224 also has channelregion 218 between the source/drain regions 214 and 216. Gate 211 isalong the channel region 218 and offset from the channel regions by gatedielectric material 213. The gate 211 may be included in a word lineWL-CT.

The selection component 220 has source/drain region 204 extending to thecell bottom 215 of capacitor 205, and has source/drain region 206extending to the digit line BL-CB. The selection component 220 also haschannel region 208 between the source/drain regions 204 and 206. Gate201 is along the channel region 208 and offset from the channel regionsby gate dielectric material 203. The gate 201 may be included in a wordline WL-CB.

As shown in the embodiment of FIG. 8, the selection components 220 and224 and capacitor 205 of the memory cell 105 are vertically stacked,which may enable memory cells 105 to be packed to high levels ofintegration.

In some embodiments, the relative orientations of digit lines BL-CT andBL-CB are reversed so that the digit line BL-CT is over a supportingbase 15 and the digit line BL-CB is over the digit line BL-CT. In suchother embodiments the illustrated capacitors 205 would be invertedrelative to the shown configuration of FIG. 8 and accordingly containershaped cell tops 230 would open upwardly instead of downwardly.

FIG. 9 illustrates a block diagram of a portion of memory 900 thatincludes memory array 100 that supports a ferroelectric memory inaccordance with various embodiments of the present disclosure. Memoryarray 100 may be referred to as an electronic memory apparatus andincludes memory controller 140 and memory cell 105, which may beexamples of memory controller 140 and memory cell 105 described withreference to FIG. 1, 2, or 4-7.

Memory controller 140 may include biasing component 905 and timingcomponent 910, and may operate memory array 100 as described in FIG. 1.Memory controller 140 may be in electronic communication with word lines110, digit lines 115, and sense component 125, which may be examples ofword line 110, digit line 115, and sense component 125 described withreference to FIG. 1, 2, or 4-7. Memory controller 140 may also be inelectronic communication with reference switch 233, isolation switch231, and switch 235, which may be examples of the reference switch 233,isolation switch 231, and switch 235, respectively, described withreference to FIG. 2 or 4-7. In some embodiments, for example,embodiments using a constant reference voltage, the memory controller140 may provide a reference signal VBLREF to the sense component 125through the reference switch 233. The components of memory array 100 maybe in electronic communication with each other and may perform thefunctions described with reference to FIGS. 1-7.

Memory controller 140 may be configured to activate word lines 110 ordigit lines 115 by applying voltages to the word and digit lines. Forexample, biasing component 905 may be configured to apply a voltage tooperate memory cell 105 to read or write memory cell 105 as describedabove. In some cases, memory controller 140 may include a row decoder,column decoder, or both, as described with reference to FIG. 1. This mayenable memory controller 140 to access one or more memory cells 105.Biasing component 905 may also provide a reference signal VBLREF tosense component 125 in some embodiments. Additionally, biasing component905 may provide voltage potentials for the operation of sense component125. The biasing component 905 may include, for example, the drivercircuit 237 configured to provide the read voltage VREAD when activated,and/or the driver circuit 239 configured to drive the digit line BL-CBto ground when activated.

Memory controller 140 may activate isolation switch 231 based onreceiving the access operation request for the ferroelectric memory cell105—that is, memory controller 140 may electrically connect memory cell105 to sense component 125. Memory controller 140 may further determinea logic state of the ferroelectric memory cell 105 based on activatingsense component 125, and write the logic state of the ferroelectricmemory cell 105 back to the ferroelectric memory cell 105.

In some cases, memory controller 140 may perform its operations usingtiming component 910. For example, timing component 910 may control thetiming of the various word line selections or cell top biasing,including timing for switching and voltage application to perform thememory functions, such as reading and writing, discussed herein. In somecases, timing component 910 may control the operations of biasingcomponent 905. For example, the memory controller 140 may control thebiasing component 905 to provide a read voltage VREAD to the digit lineBL-CT to change the voltage of the memory cell, the digit line BL-CB,and sense node A of sense component 125. The memory controller 140 maythen control the biasing component 905 to drive the digit line BL-CB toground to change the voltage of the memory cell, the digit line BL-CT,and sense node B. Following the digit line BL-CB being driven to ground,the memory controller 140 may control the sense component 125 to comparethe voltage of sense node B to the voltage of sense node A, which is ata self-provided reference voltage.

Sense component 125 may compare a signal from memory cell 105 (throughdigit line 115) with a reference voltage. As previously discussed, insome embodiments the reference voltage may be the voltage of a referencesignal VBLREF. The reference signal VBLREF may have a voltage with avalue between the two sense voltages, as described with reference toFIGS. 2, 4, and 5. In other embodiments, the reference voltage may beself-provided, for example, using as a reference voltage the voltage ofa sense node resulting from biasing a memory cell 105. Upon determiningand amplifying the voltage difference, the sense component 125 may latchthe state, where it may be used in accordance with the operations of anelectronic device that memory array 100 is a part.

FIG. 10 illustrates a system 1000 that supports a ferroelectric memoryin accordance with various embodiments of the present disclosure. System1000 includes a device 1005, which may be or include a printed circuitboard to connect or physically support various components. Device 1005may be a computer, notebook computer, laptop, tablet computer, mobilephone, or the like. Device 1005 includes a memory array 100, which maybe an example of memory array 100 as described with reference to FIGS. 1and 9. Memory array 100 may contain memory controller 140 and memorycell(s) 105, which may be examples of memory controller 140 describedwith reference to FIGS. 1 and 9 and memory cells 105 described withreference to FIGS. 1, 2, and 4-9. Device 1005 may also include aprocessor 1010, BIOS component 1015, peripheral component(s) 1020, andinput/output control component 1025. The components of device 1005 maybe in electronic communication with one another through bus 1030.

Processor 1010 may be configured to operate memory array 100 throughmemory controller 140. In some cases, processor 1010 may perform thefunctions of memory controller 140 described with reference to FIGS. 1and 9. In other cases, memory controller 140 may be integrated intoprocessor 1010. Processor 1010 may be a general-purpose processor, adigital signal processor (DSP), an application-specific integratedcircuit (ASIC), a field-programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or it may be a combination of these types ofcomponents. The processor 1010 may perform various functions and operatethe memory array 100 as described herein. Processor 1010 may, forexample, be configured to execute computer-readable instructions storedin memory array 100 to cause device 1005 perform various functions ortasks.

BIOS component 1015 may be a software component that includes a basicinput/output system (BIOS) operated as firmware, which may initializeand run various hardware components of system 1000. BIOS component 1015may also manage data flow between processor 1010 and the variouscomponents, e.g., peripheral components 1020, input/output controlcomponent 1025, etc. BIOS component 1015 may include a program orsoftware stored in read-only memory (ROM), flash memory, or any othernon-volatile memory.

Peripheral component(s) 1020 may be any input or output device, or aninterface for such devices, that is integrated into device 1005.Examples may include disk controllers, sound controller, graphicscontroller, Ethernet controller, modem, universal serial bus (USB)controller, a serial or parallel port, or peripheral card slots, such asperipheral component interconnect (PCI) or accelerated graphics port(AGP) slots.

Input/output control component 1025 may manage data communicationbetween processor 1010 and peripheral component(s) 1020, input devices1035, or output devices 1040. Input/output control component 1025 mayalso manage peripherals not integrated into device 1005. In some cases,input/output control component 1025 may represent a physical connectionor port to the external peripheral.

Input 1035 may represent a device or signal external to device 1005 thatprovides input to device 1005 or its components. This may include a userinterface or interface with or between other devices. In some cases,input 1035 may be a peripheral that interfaces with device 1005 viaperipheral component(s) 1020 or may be managed by input/output controlcomponent 1025.

Output 1040 may represent a device or signal external to device 1005configured to receive output from device 1005 or any of its components.Examples of output 1040 may include a display, audio speakers, aprinting device, another processor or printed circuit board, etc. Insome cases, output 1040 may be a peripheral that interfaces with device1005 via peripheral component(s) 1020 or may be managed by input/outputcontrol component 1025.

The components of memory controller 140, device 1005, and memory array100 may be made up of circuitry designed to carry out their functions.This may include various circuit elements, for example, conductivelines, transistors, capacitors, inductors, resistors, amplifiers, orother active or inactive elements, configured to carry out the functionsdescribed herein.

From the foregoing it will be appreciated that, although specificembodiments of the disclosure have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the disclosure. Accordingly, the disclosure isnot limited except as by the appended claims.

What is claimed is:
 1. A method, comprising: increasing a voltage of afirst cell plate of a capacitor to change a voltage of a second cellplate of the capacitor, a second digit line, and a second sense node;deactivating an isolation switch coupled between the second digit lineand the second sense node; decreasing the voltage of the second cellplate and the second digit line to change the voltage of the first cellplate, a first digit line, and a first sense node; driving the firstsense node to a first voltage and driving the second sense node to asecond voltage responsive to the voltage of the first sense node beinggreater than the voltage of the second sense node; and driving the firstsense node to the second voltage and driving the second sense node tothe first voltage responsive to the voltage of the first sense nodebeing less than the voltage of the second sense node.
 2. The method ofclaim 1, wherein the voltage of the first sense node is greater than thevoltage of the second sense node when the capacitor has a firstpolarization, and wherein the voltage of the first sense node is lessthan the voltage of the second sense node when the capacitor has asecond polarization different than the first polarization.
 3. The methodof claim 1, further comprising: providing a constant voltage to thesecond sense node as a reference voltage.
 4. The method of claim 3,wherein decreasing the voltage of the second cell plate and the seconddigit line includes decreasing the voltage of the second cell plate fromthe constant voltage to ground.
 5. The method of claim 1, wherein thevoltage of the second cell plate of the capacitor changes responsive tothe voltage of the first cell plate changing for a polarization of thecapacitor.
 6. The method of claim 1, wherein the second cell plate ofthe capacitor changes from an initial voltage to a first increasedvoltage responsive to increasing the voltage of the first cell plate fora first polarization of the capacitor, wherein the second cell plate ofthe capacitor changes from the initial voltage to a second increasedvoltage responsive to increasing the voltage of the first cell plate fora second polarization of the capacitor.
 7. A method, comprising:providing a read voltage to a first digit line and to a first plate of acapacitor coupled, via the first digit line, to a first sense node of asense component; increasing a voltage of the first plate of thecapacitor to change a voltage of a second plate of the capacitor; asecond digit line, and a second sense node of the sense component;deactivating an isolation switch coupled between the second digit lineand the second sense node of the sense component; driving a voltage ofthe second digit line and the second plate of a capacitor coupled to thesecond sense node of the sense component comparing at the sensecomponent a voltage of the first sense node to a reference voltage; anddriving the first and second sense nodes to a first and second voltages,respectively; based on the comparison.
 8. The method of claim 7, whereinthe reference voltage is a constant voltage provided to the second sensenode.
 9. The method of claim 7, wherein the second voltage iscomplementary to the first voltage.
 10. The method of claim 7, whereindeactivating the isolation switch coupled between the second digit lineand the second sense node of the sense component comprises: responsiveto a restore switch coupled between the first digit line and the firstsense node of the sense component being activated, deactivating theisolation switch.
 11. An apparatus, comprising: a first digit line; asecond digit line; a ferroelectric memory cell including a ferroelectriccapacitor, a first selection component, and a second selectioncomponent, the first selection component coupled between the first digitline and a first plate of the ferroelectric capacitor and the secondselection component coupled between the second digit line and a secondplate of the ferroelectric capacitor; a first word line coupled to agate of the first selection component; a second word line coupled to agate of the second selection component; a restore switch configured toactivate after the first digit line has received a read voltage; anisolation switch configured to deactivate responsive to the restoreswitch being activated after the first digit line has received the readvoltage; a sense component including a first sense node coupled to thefirst digit line through the restore switch and further including asecond sense node coupled to the second digit line through the isolationswitch, the sense component configured to latch voltages of the firstand second sense nodes; a reference switch coupled to the second sensenode and, when the isolation switch is deactivated, configured toprovide a constant reference voltage to the second sense node; a firstdriver circuit coupled to the first digit line and configured to providethe read voltage to the first digit line and the first sense node whenrestore switch is activated; and a second driver circuit coupled to thesecond digit line and, when the isolation switch is deactivated,configured to provide a ground voltage to the second digit line.
 12. Theapparatus of claim 11, wherein the isolation switch is furtherconfigured to isolate the second digit line from the second sense node,when the isolation is deactivated.
 13. The apparatus of claim 12,further comprising a memory controller configured to control the firstdriver circuit to drive the first digit line to the read voltage and todeactivate the second selection component.
 14. The apparatus of claim13, wherein the memory controller further configured to control thesecond driver circuit to drive the second digit line to ground when theisolation switch is deactivated and control the sense component tocompare the voltage of the first sense node to the voltage of the secondsense node.
 15. The apparatus of claim 11, wherein, when the restoreswitch is activated, the first sense node is configured to conductvoltage to the first digit line having the read voltage.
 16. Theapparatus of claim 15, wherein, when the restore switch is activated,the first sense node is configured to change to the read voltage. 17.The apparatus of claim 15, wherein the isolation switch is furtherconfigured to activate, when the first sense node has changed to theread voltage, to drive the first and second digit lines to complementaryvoltages.
 18. The apparatus of claim 11, further comprising: a pluralityof ferroelectric memory cells coupled to the first and second digitlines, each of the ferroelectric memory cells of the plurality offerroelectric memory cells including respective first and secondselection components.
 19. The apparatus of claim 18, further comprising:a plurality of first access lines each coupled to the first selectioncomponent of each respective ferroelectric memory cell of the pluralityof ferroelectric memory cells, the plurality of ferroelectric memorycells including the ferroelectric memory cell; and a plurality of secondaccess lines each coupled to the second selection component of eachrespective ferroelectric memory cell of the plurality of ferroelectricmemory cells.
 20. The apparatus of claim 11, wherein the ferroelectricmemory cell comprises: a first plate coupled to the first selectioncomponent; a second plate coupled to the second selection component; anda ferroelectric material positioned between the first and second plates.21. The apparatus of claim 11, wherein the first and second digit linesare vertically offset relative to one another, and the ferroelectriccapacitor vertically between the first and second selection components.